1. Field of the Disclosure
The present disclosure relates generally to a wellhead apparatus, and in particular to an annulus isolation valve for use with a tubing hanger installed inside subsea wellhead.
2. Description of the Related Art
Tubing hangers are employed in subsea wellheads used in, for example, oil and gas wells. The tubing hanger supports the tubing, or “string”, which extends down into the production zone of the well. The process of installing a tubing hanger into a wellhead generally involves positioning the tubing hanger on a landing seat in the wellhead using, for example, a running tool attached to the tubing hanger.
For a tubing hanger installed inside a wellhead, an annulus passage is generally used for monitoring pressure or communicating fluid to and from the annulus below the tubing hanger during installation of the tubing hanger (well completion) and throughout the life of a well. After well completion and before installation of the Christmas tree above the wellhead, all flow passages, including the annulus bore at the tubing hanger, must be sealed off to provide a temporary safety barrier so that the blowout preventer (“BOP”) connected to the wellhead during completion can be removed.
Traditionally the temporary barriers of the production and annulus passages of the tubing hanger are wireline plugs to be removed after the Christmas tree has been installed. Alternatively, annulus isolation valves installed at the annulus bore of the tubing hanger can eliminate at least some of the operations associated with use of the wireline plugs, including, for example, setting and removing the wireline plugs. Additionally, employing annulus isolation valves can allow the use of a monobore riser for Christmas tree installation, because the passage for annulus wireline plug retrieval is no longer required.
The challenges for using annulus isolation valves inside tubing hangers include space limitation, reliability, decreased flow rate and particle size limits imposed by decreased size of flow passages through the valves, added cost and inconvenience of employing wireline tools to open and/or close the valves, and potential flow erosion of sealing surfaces. The present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.